Old connections inspection

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jaydub

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Is there an NEC requirement or recommendation that taped connections in a gutter box should be tested or inspected at some interval?

I was recently on a team that investigated the events that led to an electrical fire that burned down the historic El Portal Market at the entrance to Yosemite National Park. The fire originated in the ?gutter? box between the overhead service connection and three individual revenue meters. The conductors connecting the meters were spliced to the service conductors using kerneys in a tandem arrangement. One phase became grounded to the cover of the gutter box burning a hole in the cover igniting combustible materials that set the building on fire. The electrical service was reliable for at least forty years and there was no record that the connections in the gutter box had ever been checked.
 
Sounds like improper installation in the first place that took 40 years to become a problem. A Megger check probably would have discovered the issue before the meltdown, but I'm not personally aware of any requirement that has the force of law that would have caused such testing to be performed. Additionally, these gutter taps to meters are often reworked over the years to add additional meters. This can often result in an already full gutter becoming overfull, compounding the problem of the poorly insulated Kearney bugs to be pressed even tighter against the gutter cover.
 
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Are you looking for ideas to prevent this in the future for similar installations? The recommendations would include Megger testing (insulation resistance testing) at a certain interval and the prohibition of unfused service conductors in the interior of Parks Department facilities. Great Britian requires that insulation resistance tests be performed annually in many types of public buildings.
 
From the Bill Rust photos and the tenant statements, it sounds like this building had a lot of deferred maintenance to begin with.
 
mdshunk said:
Are you looking for ideas to prevent this in the future for similar installations? The recommendations would include Megger testing (insulation resistance testing) at a certain interval and the prohibition of unfused service conductors in the interior of Parks Department facilities. Great Britian requires that insulation resistance tests be performed annually in many types of public buildings.
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have you done this on a large scale bldg?
i would like to know more about fire safety and resistance testing, do you have any helpful links or suggestions,

thanks
 
Pierre C Belarge said:
An infrared scan of this type of terminations/equipment would not hurt either.
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Sure enough. It's not all that clear to me, after reading the report, whether the ground fault was the primary cause or secondary to a heating issue from a poor connection in that gutter. It seems like the testing guru's like to sell IR scans with the testing "package" in any event. I wouldn't imagine there was much load on the service in the middle of the night in a building under renovation to have heated the connections enough to cause insulation failure, but who knows. Most of the load would have presumably been turned off.
 
steveng said:
have you done this on a large scale bldg?
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Yeah, a few. It's not really something I tell people I do, but it is something that is very interesting to me. It's a very time consuming task, and will always yield a long list of items for correction. Following water damage is when I've had to do it.

steveng said:
i would like to know more about fire safety and resistance testing, do you have any helpful links or suggestions,
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Can't help you there. I just fake it as I go. You'll need to get your hands on the NETA testing specs, I suppose.
 
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One of the differences in Infrared vs Meggering is that the infrared can be performed without disconnecting the power, and at maximum load. I like meggering, but sometimes it is not possible to convince the customer to shut down for preventative/predictive maintenance.


I do not have the infrared camera, but the cost of the cameras is coming down where it will not be long before a contractor can make money using them, as the cost to provide the service will also come down.
 
Marc thanks for the reply. I will be making recommendations regarding preventative measures that can be taken to prevent this occurrence in other aged buildings. I am looking for requirements I can quote in my report. I ran across a reference to maintenance intervals in NFPA70B, but a disclaimer in the introduction states the annex is ?for informational purposes only? and does not specifically address this situation. I agree that best practice would be to perform a coordinated shutdown, megger the conductors and visually inspect the connections at some interval.
 
Whether there was a heated connection, movement of the building, or insulation breakdown, the contact of the conductors to the cover was imminent. My fear is that an unsuspecting electrician inspecting these connections while energized could have lifted the cover and been injured.
 
Both meggering of the conductors and thermal testing with the gutter box cover removed would require a shutdown of power by the utility provider at the transformer on the pole. Visual inspection of the connections could be accomplished at the same time.
 
There was some construction going on in the building including replacement of sub-flooring throughout and the removal of the front porch. Either of these could have caused vibration or a building shift and therefore some movement in the box. The deferred maintenance and the intermittent interruption of lights we not contributing factors of the fire. There were plans being made to correct these issues, but would not have prevented the fire.
 
Educate me a little on how a thermal scan could have found this. How would an impending short to ground develop heat?

carl
 
I'm also having trouble on how one would use a megger to predict this. How does one meg the service side?

carl
 
coulter said:
I'm also having trouble on how one would use a megger to predict this. How does one meg the service side?
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If we are to believe that this was a straight ground fault, some insulation compromise was developing over time. The megger would have jumped out that compromised insulation and showed a bad reading before a genuine copper-to-steel ground fault developed. Matter of fact, even if it was a thermal issue that caused insulation breakdown over time, the megger would have rooted that out as well, since it seems like this thing was probably just about ready to fault out for a good while. After all, if a hard fault can develop in the middle of the night, it was probably teetering on the edge for quite a while.

I very much disagree with jaydub's estimation that deferred maintenance was not a contributing factor. Electrical testing, even if only visual, is a vital part of a building's overall maintenance program.
 
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jaydub said:
I am looking for requirements I can quote in my report.
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I don't think you'll find any actual requirements, but there are plenty of guidelines. I'm sorta surprised the Parks Servics doesn't have it's own requirements on electrical maintenance intervals. I know the Postal Service sure does, for instance.

Special message to the guys who think there's no work out there; do you see the huge potential business opportunity here?
 
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